This invention relates to semiconductor materials for use in various integrated circuit, methods of semiconductor material manufacture, and heat radiation structure for a semiconductor devices.
Semiconductor elements such as transistors and diodes are generally affected by temperature or extremely sensitive to heat. If the temperature of the environment of such an element rises, it causes the resistivity of the element to reduce, the reverse-current to increase, the output resistance to decrease and accordingly the current amplification factors to reduce. As a result, the element will ultimately cease to function.
When power is supplied to a transistor to operate it, power equivalent to the difference between its input and output is consumed as a collector loss within the semiconductor element itself. Heat is generated by this loss. That heat will also bring about the same problems as aforementioned. This has been the reason why power transistors, in particular, are provided with a cooling body or radiator (heat sink).
Moreover, with the latest progress in semiconductor technology and large scale integration of elements, there is a growing tendency toward increasing the size of the element itself and mounting a plurality of semiconductor chips on one package to provide a multi-chip package. Consequently, it has become inevitable that the size of the IC package carrying those semiconductor chips increases. It has become important to match the thermal expansion coefficients of materials constituting the package and thermal design relative to the semiconductor elements.
For instance, the thermal expansion coefficient of materials constituting a semiconductor substrate must be at least different from that of the semiconductor element so that distortion due to thermal stress can be prevented. Accordingly, there have been used, as a material having a small thermal expansion coefficient, an Ni alloy such as cobale (29% by weight of Fe-Ni 17% by weight of Co-Fe) or 42 alloy (42% by weight of Ni-Fe), or ceramics such as alumina or fosterite.
Recent progress in semiconductor technology has led to the introduction of large-sized elements and increased integration. These have presented problems of heat radiation as well as the difference between thermal expansion coefficients. When the size and integration of elements are increased, materials in use need to provide not only a smaller difference between thermal expansion coefficients but also greater heat radiation.
There have been proposed, as materials satisfying both characteristic requirements, beryllia-ceramics, tungsten and molybdenum.
However, since beryllia-ceramics are highly poisonous, they are practically unusable in view of safety and environmental problems.
Also, since molybdenum and tungsten are rare metals and locally distributed, they are highly expensive. A semiconductor device using such metal materials will be expensive to produce. In addition, since such metals are relatively dense metals (19.3 g/cm.sup.3 and 10.2 g/cm.sup.3 for W and Mo, respectively), they have disadvantages including heavy weight and the relative difficulty of undergoing mechanical processing.
In view of excellent thermal conductivity, copper or aluminum alloys have been used as a heat sink (heat radiation plate) when thermal design of semiconductor devices is made. However, thoses alloys are normally a bad match, in terms of a thermal expansion coefficient, for ceramics such as Al.sub.2 O.sub.3 and SiC, metal materials such as Fe-Ni-Co alloy, Fe-Ni alloy, W and Mo, or compound materials prepared from the aforementioned metal and copper when the latter is used as a housing material for semiconductor devices. Because of this mismatching a bend or curvature is produced when they are mated with a substrate during the manufacturing process.